1. Field of the Invention
The present invention relates to an electronic component having wires, such as a wire wound type chip coil.
2. Description of the Related Art
Conventionally, a chip coil having stability at the time of mounting is disclosed in Unexamined Japanese Patent Publication 10-312922. In this chip coil, an electrode includes an underlying metal layer, an Ni-plated layer, and a Sn-plated layer. The end of the wire is embedded in the Sn-plated layer by thermal compression bonding.
In this kind of the chip coil, the Cu of the wire is melted and penetrates into the Sn in a molten solder and the Sn-plated layer at the time of mounting (reflow soldering), and the thickness of the wire is greatly reduced and becomes very thin. In some cases, the wire may be eluted and broken. Usually since the wire constituting a coil has an insulating coating film, if the insulating film has a high heat resistance, eluting of Cu can be avoided. However, since an end portion of the wire, at which the insulating film is removed, is connected to the electrode, the end portion of the wire without the insulating film is eluted into Sn in a molten solder and the Sn-plated layer. The recently required size reduction of an electronic component requires that the wire be thinner. Thus, it is necessary to prevent the wire from becoming thin and to prevent the wire breakage caused by the fact that Cu of the wire is eluted.
In order to overcome the problems described above, preferred embodiments of the present invention provide an electronic component that prevents Cu of a wire from eluting into Sn in molten solder, a Sn-plated layer or other layer from the wire.
According to one preferred embodiment of the present invention, an electronic component includes an insulating body having an electrode provided thereon, and a wire made of Cu wound on the insulating body, an end of the wire is fixed to the electrode, wherein the electrode includes a plurality of conductive layers, and at least one of the conductive layers prevents Cu from eluting out of the wire.
An eluting prevention layer (at least one of the conductive layers which prevents Cu from eluting out of the wire) decreases the dissolution rate or stops the dissolution itself with Cu of the wire, and Sn in the molten solder and the plating layer. A suitable material for the eluting prevention layer is Cu. The fact that one layer of the electrode includes Cu results in the state that Cu is eluted into Sn in advance, and Cu of the wire is prevented from eluting. Cu for preventing elution is preferably provided as an Snxe2x80x94Cu alloy layer or a single Cu layer. Preferably a Cu content of Snxe2x80x94Cu alloy layer is about 0.5-30 wt %. Generally, the temperature at the time of the soldering is about 240xc2x0 C. to about 260xc2x0 C. Regarding the eutectic concentration of Cu and Sn in this range of temperature, that of Cu is about 0.5 wt % to about 0.6 wt %. Accordingly, when the content of Cu is at least 0.5 wt %, elution of Cu is prevented beyond that content. When the content of Cu exceeds 3.0 wt %, solderability deteriorates. The inventors have discovered that Ni is a material which also prevents elution of Cu. The Cu elution preventing effect is sufficiently achieved by using a Snxe2x80x94Ni alloy layer.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.